feat: Todo altijd gekoppeld aan product backlog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/todos/route.ts

@@ -4,6 +4,7 @@ import { z } from 'zod'
 
 const bodySchema = z.object({
   title: z.string().min(1, 'Titel is verplicht').max(500),
+  product_id: z.string().min(1, 'Product is verplicht'),
 })
 
 export async function POST(request: Request) {
@@ -21,9 +22,17 @@ export async function POST(request: Request) {
     return Response.json({ error: parsed.error.flatten() }, { status: 400 })
   }
 
+  const product = await prisma.product.findFirst({
+    where: { id: parsed.data.product_id, user_id: auth.userId, archived: false },
+  })
+  if (!product) {
+    return Response.json({ error: 'Product niet gevonden' }, { status: 404 })
+  }
+
   const todo = await prisma.todo.create({
     data: {
       user_id: auth.userId,
+      product_id: parsed.data.product_id,
       title: parsed.data.title,
     },
   })